This invention relates to a vehicle utilization fuel system for use primarily in internal-combustion road vehicles.
Multiple-tank fuel systems heretofore known employ a plurality of tanks, with the fuel from one tank being passed to another tank through crossover lines coupled to the bottom walls of the tanks. These crossover lines are generally the lowest parts of the vehicle, since flow between the tanks depends upon gravitational forces, and are generally more susceptible to accidental breakage due to debris on the highway or other obstructions which may impact against the below-tank crossover line.
Fuel tank utilization systems, such as shown in U.S. Pat. No. 3,981,321, were developed in which an above-tank crossover line was employed. This patented system requires feed lines of about equal length, about equal inner diameters, and about equal fuel flow restrictions, and requires return lines separate from the feed lines, also each having about equal length, about equal inner diameters, and about equal fuel flow restrictions. This system also removes fuel simultaneously from all of the tanks.
Other systems involve expensive mechanical parts, such as selector valves, for selecting the return and draw from the tanks independently. Each time a fitting or valve is added to a fuel tank system, the possibility of creating an air leak increases. An air leak in a vehicle fuel system, particularly a diesel-powered, internal-combustion system, creates considerable difficulty for the operator to seal the air leak and reinitiate suction and flow of fuel to the diesel engine. If the engine on a large truck, such as a tractor-trailer truck, for example, is deprived of fuel while under way, it will stop the engine and damage the fuel pump.
The same stoppage of the engine and damage to the fuel pump can also occur for any of the fuel utilization systems which draw simultaneously from the multiple tanks. By drawing simultaneously from the multiple tanks, air can be drawn when the higher tank is running low in fuel. If one tank is at a lower elevation than the other, the fuel in the higher tank will be depleted prior to the fuel in the lower tank, allowing the draw tube to suck air, thus depriving the engine and pump of fuel. Tractor-trailer trucks, for example, are frequently driven on crowned or cambered roads, or the engines are idling while the truck is resting on a shoulder. In the United States road system, at least, the right-hand tank, if the tanks are transversely spaced on the vehicle, will thus generally be at a lower elevation than the left-hand tank. In foreign countries such as England, where the vehicles are driven on the left side of the road, the left-hand tank will frequently be below the right-hand tank.
Hereinafter, the term "primary tank" will refer to the tank which is on the lower elevation, the right-hand tank in a U.S. road vehicle and the left-hand tank on a vehicle driven in a country where the vehicle operates on the left-hand side of the road. The other tank will be termed a "secondary tank."